ArticleslgStudy

science

Buoyant density centrifugation

Buoyant density centrifugation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Buoyant density centrifugation rather than just read about it. In short: Buoyant density centrifugation (also isopycnic centrifugation or equilibrium density-gradient centrifugation) uses the concept of buoyancy to separate molecules in solution by their differences in density. Implementation Historically a cesium chloride (CsCl) solution was often used, but more commonly used density gradients are sucrose or Percoll.

Buoyant density centrifugation — main illustration
Buoyant density centrifugation — illustration

Key takeaways

  • Buoyant density centrifugation belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Buoyant density centrifugation to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Buoyant density centrifugation from memory before moving on to harder problems.

Reference excerpt

Buoyant density centrifugation (also isopycnic centrifugation or equilibrium density-gradient centrifugation) uses the concept of buoyancy to separate molecules in solution by their differences in density.

Implementation Historically a cesium chloride (CsCl) solution was often used, but more commonly used density gradients are sucrose or Percoll. This application requires a solution with high density and yet relatively low viscosity, and CsCl suits it because of its high solubility in water, high density owing to the large mass of Cs, as well as low viscosity and high stability of CsCl solutions.

The sample is put on top of the solution, and then the tube is spun at a very high speed for an extended time, at times lasting days. The CsCl molecules become densely packed toward the bottom, so a continuous gradient of layers of different densities (and CsCl concentrations) form. Since the original solution was approximately the same density, they go to a level where their density and the CsCl density are the same, to which they form a sharp, distinctive band.

Isotope separation This method very sharply separates molecules, and is so sharp that it can even separate different molecular isotopes from one another. It has been utilized in the Meselson-Stahl experiment.

DNA separation Buoyant density of the majority of DNA is 1.7g/cm3 which is equal to the density of 6M CsCl solution. Buoyant density of DNA changes with its GC content. The term "satellite DNA" refers to small bands of repetitive DNA sequences with distinct base composition floating above (A+T rich) or below (G+C rich) the main component DNA.

See also Isopycnic Satellite DNA

References

Further reading Schildkraut, Carl L.; Marmur, Julius; Doty, Paul (1962). "Determination of the base composition of deoxyribonucleic acid from its buoyant density in CsCl". Journal of Molecular Biology. 4 (6): 430–443. doi:10.1016/S0022-2836(62)80100-4. ISSN 0022-2836. PMID 14498379. James Greene (25 June 1998). Recombinant DNA Principles and Methodologies. CRC Press. pp. 278–. ISBN 978-0-8247-9989-2.

Illustrations

Buoyant density centrifugation: Electron microscope image of canine parvovirus isolated using buoyant density centrifugation
Electron microscope image of canine parvovirus isolated using buoyant density centrifugation
Buoyant density centrifugation: Caesium chloride (CsCl) solution and two morphological types of rotavirus. Following centrifugation at 100 g a density gradient forms in the CsCl solution and the virus particles separate according to their densities.
Caesium chloride (CsCl) solution and two morphological types of rotavirus. Following centrifugation at 100 g a density gradient forms in the CsCl solution and the virus particles separate according to their densities.

Worked examples

Example 1 — a first encounter with Buoyant density centrifugation

Start with the simplest possible case. Write down what Buoyant density centrifugation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Buoyant density centrifugation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Buoyant density centrifugation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Buoyant density centrifugation

In research
Buoyant density centrifugation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Buoyant density centrifugation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Buoyant density centrifugation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Laboratory techniques, Separation processes, so understanding it makes those chapters shorter.
In everyday life
Look for Buoyant density centrifugation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Buoyant density centrifugation in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Buoyant density centrifugation means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Buoyant density centrifugation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Buoyant density centrifugation in simple terms?

Buoyant density centrifugation (also isopycnic centrifugation or equilibrium density-gradient centrifugation) uses the concept of buoyancy to separate molecules in solution by their differences in density. Implementation Historically a cesium chloride (CsCl) solution was often used, but more common…

Why does Buoyant density centrifugation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Buoyant density centrifugation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Buoyant density centrifugation.

Tags

  • Laboratory techniques
  • Separation processes

Keep exploring